The present invention relates to a multi-nozzle combustor having a pilot nozzle for flame retention in the center and a plurality of main nozzles around the pilot nozzle, and more particularly, to a multi-nozzle combustor suitably used as a gas turbine combustor.
FIG. 1 is a sectional view of a conventional combustor. This combustor comprises a pilot nozzle 3 in its central portion and a cone 4 for flame retention around it. A plurality of main nozzles 1 are arranged in the circumferential direction between the cone 4 and an inner cylinder 5.
Each main nozzle 1 includes a shaft 6 for fuel supply and a nozzle guide 2. FIG. 2 is an enlarged view showing one main nozzle 1 and its surroundings. As shown in FIG. 2, a region for flame propagation from a pilot flame to a main fuel is formed between the flame-retention cone 4 of the pilot nozzle 3 and the inner cylinder 5. In this propagation region, a distribution 12a of the fuel ejected from the main nozzle 1 is an uneven distribution, involving a fuel-lean region corresponding to a flow area 11 behind the shaft 6 and a fuel-rich region 12b around it.
Since the fuel is ejected at a certain fuel ejection angle 10 to an airflow, as shown in FIG. 2, the distribution 12a of the fuel ejected from the main nozzle 1 between the flame-retention cone 4 and the inner cylinder 5 involves a fuel-overrich region.
As shown in FIG. 2, moreover, the length of a mixture-evaporation region 16 from a fuel ejection position to a firing position is so short that a liquid fuel cannot be mixed satisfactorily with air. Accordingly, there exist also microscopic fuel-overrich regions.
When a gas turbine is subject to a high load, furthermore, the fuel concentration has a distribution 12a such that it is low in the region around a main nozzle shaft center 7 and higher on the wall side, as shown in FIG. 3A. When the turbine load is low, on the other hand, the fuel concentration has a distribution 12b such that it is high in the region around the shaft center 7, as shown in FIG. 3B.
In the fuel nozzle of the conventional combustor, as described above, the use of the fuel supply shaft 6 entails the existence of the fuel-rich region 12b.
The gas turbine combustor is subject to the problem of reduction of NO.sub.X in exhaust gas. An NO.sub.X generating region is a region in which the fuel is overrich and its concentration is locally high. Since the fuel distribution of the conventional fuel nozzle is uneven, it involves the fuel-rich region 12b, as shown in FIG. 2, so that the delivery of NO.sub.X is substantial.
Further, the fuel distribution varies depending on the load. When the load is high, a flame propagation 14 can be effected smoothly with the main fuel distributed very close to a pilot flame 19, as shown in FIG. 3A. When the load is low, however, the main fuel is distributed at a distance from the pilot flat 19, so that a flame propagation 18 from the pilot flame 19 to the main fuel cannot be effected smoothly, as shown in FIG. 3b, and therefore, a combustible is left inevitably.